Method and apparatus for contention management in a radio-based packet network

ABSTRACT

In a mesh communication network, a poll request protocol (PRP) is provided in which a special packet is broadcast by the congested node when it is ready to provide services. The controlling node (usually the more congested node) broadcasts a packet to request poll signals from nodes desiring resources of the controlling node. The contending nodes then have equal chances to request the services of the controlling node by sending poll signals. The controlling node can then arbitrate the requests, determine the most fair and efficient use of its resources, and broadcast a scheduling packet to inform the contending nodes when to inform the contending nodes of controlling node scheduling. The contending nodes then send their packets to the controlling node without lost packets caused by congestion collisions. The controlling node can then send data to the contending nodes also without lost packets.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/894,843, filed Jun. 27, 2001, and entitled “METHOD AND APPARATUS FORCONTENTION MANAGEMENT IN A RADIO-BASED PACKET NETWORK,” the completedisclosure of which is herein incorporated by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK NOT APPLICABLE BACKGROUNDOF THE INVENTION

This invention relates methods and apparatus for regulating trafficamong contending nodes, being particularly advantageous in a wirelessmesh packet radio network system.

In a meshed communication system, packets will favor routes whichhistorically have provided the best performance. As traffic increases,previously acceptable paths will provide degraded performance because ofcongestion unless alternate, normally slower paths are used or unlesscommunication protocols provide dynamic relief at the affected nodes bychanging their characteristics to be more efficient under load.

Meshed packet networks are one of several types of data communicationnetwork architectures that support packet communication. Other majortypes are star (e.g., cellular or 10-baseT) and bus (e.g., computerbackplane). Mesh networks have several advantages over otherarchitectures for providing high-capacity, high reliability datacommunication over a large area and to a large number of users.

In a radio-based packet mesh network, an interconnected mesh of datapacket sending and receiving nodes collectively captures, routes anddelivers data packets in a shared medium. The sharing of this mediumresults in mutual interference and loss of some packets due tocollisions caused by congestion. When a packet is lost, it must beretransmitted, which causes further congestion in the network and causesfurther packet loss. The packet loss and retransmission consume thelimited bandwidth that is used to provide the communication services thenetwork was installed for. It is desirable to minimize this loss ofpackets so that the network can provide a greater level of performanceto the greatest number of users of the network.

Any transmissions or packets that are sent that do not deliver data tothe users of the network decrease the efficiency of the network. Thehigher the efficiency of the network, the more useful work it isperforming and the higher its intrinsic value. It is desirable thereforeto minimize the overhead packets and transmissions that the protocoluses to communicate to other nodes and to maximize the number of packetsthat actually deliver data to the users of the network.

As a network becomes more congested and it attempts to deliver morepackets than it is capable of, it is desirous that a user get their fairshare of the resources. In typical packet networks some users will befavored over others because of the topology of the network or the timedistribution of the traffic that they are sending. The network protocolsshould be designed so that the bandwidth is allocated in a fair andequitable manner regardless of these circumstances.

In a network with intelligent nodes, each node works to manage thetraffic through itself. There are several known methods by which thismight be done, each has disadvantages, as described below, over theinvention described in this patent:

Polling: The controlling or contended node may poll each of the nodescontending for services. The controlling node has imperfect informationregarding the servicing needs of the contending (or slave) nodes.Bandwidth used by the controlling node determining if demand exists isoverhead which should be minimized. Particularly in a meshed radionetwork, the extra transmissions can cause further degradation ofservices because they can increase congestion for multiple nodes.

CSMA/CD: With the Carrier Sense Multiple Access/Collision Detectprotocol each node contending for the services transmits (polls) andawaits a response. If the expected acknowledgment is not forthcoming,each of the contending nodes “backs off” or delays an algorithmic amountof time and then retries the poll transmission. This technique iscommonly used in wired LAN topologies where all nodes are in reliablecommunication with each other and thus can reliably hear theacknowledgment to the poll and know when not to transmit. Unfortunately,in many topologies, because of unreliable communication channels, eachnode has only imperfect information about the state of the targetednode. In this case, only the successful contender (if there was one) isguaranteed to know exactly when the contended node will be free toreceive another packet (after the successful node has finishedtransmitting its packet).

CDMA: With Code Division Multiple Access, contending nodes transmit bymeans of a limited set of orthogonal codes. These codes can beselectively detected by decoding each transmission with its own codingsequence. This technique can be used for sending packets from multiplesimultaneously transmitting mobile units on the same frequency channelwhere relative timing can be maintained. However, the frequency channelbandwidth must be increased to handle the additional transmissions. Thelimitations of this technique are manifold: the processing gain of thecoding used limits the number of simultaneously transmitting mobileunits. For greatest capacity, the power level of the mobile units mustbe controlled to be nearly uniform when received at eachmultiple-station receiving node such as a mobile telephone cellsite.This requires additional protocol overhead which reduces the efficiencyof the network.

It is well known that CSMA/CD does not work efficiently as acongestion-limiting scheme for meshed radio networks because of thenature of radio where all nodes cannot ‘see’, or simultaneouslycommunicate with, each other and thus are not able to reliably avoidburst transmissions which block each other. This is a particularlysevere problem when the applied load of traffic is large relative tocongested node capacity.

Other, more sophisticated protocols (such as GAMA-PS as described byAndrew Muir and J. J. Garcia-Luna-Aceves, “An Efficient Packet SensingMAC Protocol for Wireless Networks”, MONET 3(2):221-234 (1998)) workbetter as a congestion-limiting scheme for radio based systemscommunicating with each other on a single frequency channel (analogousto a wire). They are; however, unable to handle multiple channels andthus take advantage of the inherent efficiencies available in a meshednetwork where multiple packets can be sent between different pairs ofnodes simultaneously. Protocols designed to handle multiple channels,such as those used for optical networks, have not been designed toefficiently handle unreliable channels, such as those typical in radionetworks. Other protocols (such as PRMA as described by D. J. Goodman,R. A. Valenzuela, K. T. Gayliard and B. Ramamurthy, “Packet ReservationMultiple Access for Local Wireless Communications,” IEEE Transactions onCommunications, (August 1989) require even more complicated collisiondetection that is not cost effective or is not available with currentradio technology.

The following patents and publications provide further backgroundinformation:

U.S. Pat. No. 5,384,777 Ahmadi, et. al. Jan. 24, 1995, entitled“Adaptive Medium Access Control Scheme for Wireless LAN”; Ahmadi, Hamid;Bantz, David F.; Bauchot, Frederic J.; Krishna, Arvind; La Maire,Richard O.; Natarajan, Kadathur S.; assigned to IBM Corporation filedApr. 19, 1993. It discloses an evidently inflexible fixed slot master(base)/slave contention reduction scheme. Access is random access, butthere is no teaching of mini-slot categories.

ANSI/IEEE Standard 802.11, 1999 Edition. “IEEE Standards for informationtechnology; Telecommunications and information exchange between systems;Local and metropolitan area networks; specific requirements; Part II:Wireless LAN Medium Access Control (MAC) and Physical Specifications. Itteaches a time-based scheme dependent on a single base-station withwhich all nodes must be in contact.

U.S. Pat. No. 5,471,469: Nov. 28, 1995, entitled. “Method of resolvingmedia contention in radio communication links”; George Flammer and BrettGalloway, assigned to Metricom of Los Gatos, Calif. This disclosureteaches a novel way of reducing contention in a frequency hopped packetradio network but under load (heavy contention) is an inefficient andunfair protocol.

U.S. Pat. No. 5,297,144: “Reservation-based polling protocol for awireless data communications network”; Gilbert; Sheldon L., Heide;Carolyn L., Director; Dennis L., assigned to Spectrix Corporation ofEvanston, Ill. This teaches an inefficient polling mechanism that doesnot take advantage of the broadcast nature of wireless and requiresmultiple handshakes between each data transfer.

U.S. Pat. No. 5,818,828: Oct. 6, 1998 entitled “Hybrid multiple accessprotocol for wireless frequency hopping microcells with adaptivebackhaul and heartbeat”; Packer; Robert L., Xu; Milton Y., Bettendorff;John, assigned to Metricom, Inc., Los Gatos, Calif. This disclosureteaches a polling system that requires a Master/Slave relationship to beset up and is inefficient in requiring a poll for every data packet sentand a poll to determine if there is any data available to send.

What is needed is an improvement in communication protocols for meshnetworks with multiple channels that can perform efficiently withimperfect channels and provide increased throughput and fair allocationof resources, even under load, with minimal increase in controloverhead.

BRIEF SUMMARY OF THE INVENTION

According to the invention, in a mesh communication network such as aradio-based packet network, a poll request protocol (PRP) is implementedin which a special packet or datum of information is broadcast by thecongested node when it is ready to provide services. Specifically, thecontrolling node (usually the more congested node) broadcasts a packetrequesting poll signals from nodes desiring resources of the controllingnode. The contending nodes then have equal chances to request theservices of the controlling node by sending poll signals. Thecontrolling node can then arbitrate the requests, determine the mostfair and efficient use of its resources, and broadcast a schedulingpacket to inform the contending nodes of when to send their packets andinform the contending nodes that the controlling node will send data tothem. The contending nodes then send their packets as scheduled to thecontrolling node without lost packets caused by congestion collisions,the controlling node can then send data to the contending nodes alsowithout lost packets caused by random access collisions with thereceiving nodes.

The present invention is an advance on the typical method and apparatusutilized in a mesh network among communicating nodes that experiencecongestion due to unavoidably high traffic levels. The invention alsoprovides advantages in efficiency and fairness, particularly in a meshedpacket radio network system where broadcast must be used and bandwidthis a very limited resource.

This technique is particularly advantageous when coordinating theresource demands of an indeterminate number of nodes, each generatingsuch demand asynchronously. In this case (which is typical of packetradio networks) the broadcast packet from the contended node providesidentical information to all of the potential client nodes; such astiming, load, and availability, thereby giving each contending node anequal view of the controlling node's state. This allows each contendingnode an equal chance of using the controlling node's resources, thuspreventing resource capture by lucky or favored nodes.

Widespread implementation of PRP increases the network carrying capacityby substantially reducing poll packets over the prior art and limitingthem to the active clients of the contended node, the PRP master.

Unlike prior art polling methods, which operate within the master/slaveparadigm, where the master polls the slave units, asking them if theyhave data for transfer and/or whether they are present to receive a datatransfer to them; PRP limits the number of polls sent and received. Inthe prior art, the slave units either respond to polling whether or notthey have data or decline to respond if they have none. It is worthwhileto note that the master interrogates the slaves through the polling.Polls unheard or which fall upon slaves with no data to send areexamples of expensive spectrum wasted. Since the master (being thecontended resource) is typically in a propagationally favored locationor configuration, wasted packet from the master radio node are maximallydeleterious to the network as a whole.

Since the PRP packet is broadcast, and thus available to a large numberof interested and affected nodes, the number of Polls and the number ofwasted packets in the media is minimized, leaving greater networkcapacity for message traffic. Since the radios responding to the singlebroadcast PRP packet, i.e., doing the polling, are often subscriberdevices with a smaller radius of interference, their polls are lessdeleterious to the network, thus leaving greater network capacity forcommunicating.

Since all requested polls are received in the same phase, prioritizationof the traffic around and through the contended node is optimizable somultiple levels of service are possible. This is an advance over priorart in polling which did not allow for scheduling or priority.

Since a PRP master can easily listen for another PRP master, and the PRPsystem operates asynchronously, all nodes in the network, even portablenodes, can use PRP to control their own congestion. In particular,network software code is more manageable since all nodes can run thesame algorithm and all nodes react similarly.

The invention will be better understood upon reference to the followingdetailed description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a mesh radio system for illustratingcontention resolution according to the invention.

FIG. 2 is a time-flow chart according to the invention.

FIG. 3A, 3B, 3C are graphical descriptions of the types of packets usedin the invention.

FIG. 4 is a state diagram of the invention.

FIGS. 5A-5E is a detailed flow chart of one aspect of the inventionrelating to the PRP master.

FIGS. 6A-6C is a detailed flow chart of another aspect of the inventionrelating to the PRP client.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, it is often the case in a mesh network 10 thatmultiple radios of a selected type, namely wireless modems 12 orpoletops 14, wish to send their packet to the same node A. The modems 12send packets to and receive packets from various poletops 14. Thepoletops 14 send and receive packets to and from a poletop 14 at Node Athat is connected to the wired infrastructure backbone 16. Each group16, 18, 20, 22 of radios participating in a PRP group is logicallyassociated by communication with a common server at Node A, Node B, NodeC and Node D (as circled). One of the PRP groups 22 can be defined asconsisting of only poletop units associated with a server at node A. Thenode with contention above an indeterminate threshold representingcongestion is the controlling node for its PRP group; all of the otherradios must request its service in order to be functional. In the otherthree groups, the poletop (at nodes B, C, or D) the nodes are also undercontention and the radios in the respective associated PRP groupsrequest service. Thus a node may be a controlling node in one PRP group,while at the same time it could be a requesting node in another PRPgroup.

FIG. 4 is a state diagram of a method according to the invention. Thereare three basic states or modes involved in the implementation. First anonPRP mode 1, in which any node detects that it may benefit from theincreased overhead of congestion management protocol (transition StepA). It may determine this from a variety of sources, such as clientnodes that can report their “success rate” or “desperation index” to thecontended node (when they finally get to give the node some data).Alternatively, a congested node can determine for itself that the levelof traffic it is carrying must be generating delays and enter theStartPRP mode (state) itself.

Once it is determined that the PRP mode is appropriate, the congestednode goes into the StartPRP state 2 and advertises its changed state viaany mechanisms it has available to do so (transition Step B). Thesemeans include:

Broadcast packets that indicate state, timing, and traffic level.

Bits set in the header of packets exchanged in the course of ‘normal’communication.

“Assumptions” made by other nodes in response to local failuresgenerated and tabulated in the course of data traffic handling.

Thereupon, the node is in the PRP state 3 and the PRP mechanism is usedto resolve contention and manage client radios in the vicinity(transition Step C).

When a node determines that it is no longer under contention, e.g., itreceives no polls after a poll request or it determines that therequested services can be handled more efficiently without PRP, it exitsthe PRP state and returns to the NonPRP state 1 (via transition Step D).

FIG. 2 is a time-flow diagram of a method of the invention showing ingreater detail the exchange of packets between the various nodes whenthe contended node is in PRP state 3. When in the PRP state 3, a nodebroadcasts a Poll Request Packet (PRP) to solicit polls from the clientsthat actively have traffic to offer (Step C1). Since client nodes canvary widely in number and in traffic profiles, the Poll Request Protocol‘master’ can dynamically assign bandwidth to clients for poll requestsand data packets under control of its particular selection algorithms.The number of mini-slots for Polls can be increased and distributedamong different classes of traffic.

The contending nodes that have not been scheduled to send data in thePRP packet send Polls to the master node requesting to send a datapacket. The Polls are targeted to fall into one of several mini-slots intime after the end of the PRP packet according to the algorithmsdynamically specified in the PRP packet. Several mini-slots may beassigned to a particular class of clients by the PRP master to reducecontention for that class of clients. The clients randomly target thepolls into one of the designated mini-slots. (Step C2).

The PRP packet and, after receipt of the polls, the ContentionResolution Packet (CRP), lay out the rules of transmission among nodesdesiring to transmit to the PRP master (Step C3). These are heard by alland provide useful client-client transmission information. [Note that aPRP master may be (and usually will be) a client to another PRP master.]

This mechanism has many advantages. By this means the client/mastercommunications are synchronized, communication in the affected communityof radios is freed of collisions, and priorities can be directlyenforced so that high priority exchanges are completed before lowerpriority traffic is started.

Specifically, transmit/receive phases are enabled (Step C4). In thismode, all traffic to be sent to the master can be consecutively sentbefore the master radio node transmits data back. This mode permitsreduction or elimination of “turn around time” as the clients and masterradios switch back and forth between transmit and receive.

During this mode, availability and traffic load are announced, as wellas acknowledgments for correctly received data packets (Step C5).Thereby, the “losers” of the polling competition for the attention ofthe master radio have useful knowledge by which they can decide whetherto select another node for forwarding their traffic.

The clients that received data packets as schedule in the CR Packet,transmit their scheduled acknowledgments of the received data packetsback to the controlling node (Step C6). Thus a complete PRP cycle iscompleted and data is transferred between a controlling node undercontention to a plurality of requesting nodes in a fair and efficientmanner.

The node then determines if it is still in poll-request mode. If not, itproceeds to transition Step D, if it is still under contention. Forinstance, multiple clients have just requested to transmit data to it inthis PRP cycle, then the node stays in PRP mode. Before starting a newPRP cycle, the node can attempt to send data that it has that was notdestined to any of the requesting clients. (This data would have beensent in Step C4). For instance, some of the data that a requestingclient has just sent may be forwarded further along in the network.

The whole PRP cycle then repeats, starting at step C1.

The Poll Request Protocol (PRP) has been designed with a number ofoptional fields:

The PRP packet itself can be sent upon return from completion ofoff-channel traffic carrying (sent as an “I'm back” packet).

The PRP master allocates its resources by specifying the number andpermitted occupants of the (smaller) poll minislots. These minislots areshort periods in time where specific nodes or classes of nodes arepermitted to poll the PRP master. By specifying the number of theseslots and their possible occupants, the PRP master can arbitrarilyrefine the performance of the radios by using it as a forwarding orterminus link.

The client radios receive the results of their polls in a subsequentcontention resolution packet. This form of contention resolution packethas timing and frequency information in it that the contending clientsmust follow if they are to utilize the PRP master.

FIG. 5A-5E is a flow chart of the invention showing more detail of thestates. The node enters the PRP mode (State 3 of FIG. 4, Step 5A-1 ofFIG. 5A) and detects for packets on the nonPRP send queue (5A-2); ifyes, it sends the nonPRP data (5A-3) and proceeds; otherwise it simplyproceeds to determine the number of minislots required for pollers(“clients”) (5A-4). The minislots are timeslots allocated during whichclients are permitted to contact the node. The node then determines ifany of the pollers are already assigned minislots (5A-5). Next the nodedetermines its average load for the past time period (5A-6) to allow theuse of an algorithm to advertise the allocation of minislots. It thenconstructs a Broadcast Request Packet (FIG. 3A) (5A-7) and thereuponsends the Broadcast Request Packet (5A-8).

Referring to FIG. 5B, the node thereafter listens during a contentionminislot for a Poll Packet (FIG. 3B) (Step 5B-1) and if it does hear aPoll Packet (5B-2) it records the Poll Packet (5B-3), increments a firstcounter of the number of minislots listened to 5B-4). If it does nothear a Poll Packet, it merely increments the counter value (5B-4). If itsenses that the counter value is equal to the number of contentionminislots, it continues on (5B-5); otherwise it continues to listen(5B-1).

Referring to FIG. 5C, it then continues by listening during one or morereserved minislots for a Poll Packet (FIG. 3B) (Step 5C-1) and if ithears a Poll Packet (5C-2) responds as before by recording the PollPacket (5C-3), incrementing a second counter (5C-4) and tests to see ifthe second counter value equals the number of reserved minislots (5C-5),repeating the process until it does equal. When it does equal, itconstructs a Contention Resolution Packet (FIG. 3C) (Step 5C-6), whichis used to carry the sending transmit start time to clients and pollers.It then broadcasts this Contention Resolution Packet (5C-7).

Referring to FIG. 5D, the node next sets up and triggers a timer to setthe maximum listening time for the end of an expected variable lengthdata packet (FIG. 2 at C4) (Step 5D-1). This could be a timer for eachdata packet or it could be a timer for all expected packets in asequence. The node then listens for the Data Packets (5D-2) and if itdoesn't hear one (5D-3) it checks for time expiration (5D-6) and eitherrepeats or times out. If it hears a Data Packet, it records the DataPacket (5D-4) and checks to see if this is the last Data Packet tolisten for (5D-5). Once it has completed listening, it sends theDesignated Data Packets directed to the clients (5D-7), then checks allreceived packets for correctness, deleting those that are incorrect(5D-8) before continuing.

Referring to FIG. 5E, the node thereafter constructs a single BroadcastAcknowledgment Packet (FIG. 2) which carries an acknowledgment for everycorrectly received packet, plus designating a set of reserved minislotsfor each client wishing to reply with more data (Step 5E-1), and itbroadcasts this packet (5E-2), thereafter listing for receiveacknowledgments (FIG. 2) (Step 5E-3). For each acknowledged packet, itdeletes the corresponding packet from its send queue (5E-4) so it willnot be resent, places each received packet that is destined for a pollerin the PRPsend queue (5E-5), and then it places all other packets in thenonPRPsend queue (5E-6). If there is nothing placed in these queues aschecked (5E-7), it exits the PRP mode (state 3 FIG. 4, Step 5E-8);otherwise it repeats the process from the beginning of the sequence.(FIG. 5E to FIG. 5A, Step 5E-9).

Referring to FIGS. 6A-6C, the flow chart for a PRP client is described.Its state diagram is not shown, but the states are evident as beingcorrespondence to the state diagram of FIG. 4. In FIG. 6A, the clientnode enters a PRP state corresponding to the same state as the servernode (Step 6A-1), sets up a timer for PRP timeout on the server node(6A-2) and monitors for timer expiration (6A-3). If the timer expires,the client leaves the PRP state corresponding to the state in the servernode (6A-4).

Until the timer expires, the client listens for the Broadcast PollRequest Packet (6A-5) and if it doesn't hear it, continues with otherwork (6A-10). When it hears the Broadcast Poll Request Packet, it checksfor a reserved contention minislot for itself (6A-7). Upon finding noneit sends a Poll Packet in any random contention minislot (6A-8) andcontinues. Otherwise it sends a Poll Packet in the specified reservedminislot (6A-9) and continues.

Referring to FIG. 6B, the client then listens for the BroadcastResolution Packet (6B-1) and finding none (6B-2) continues; otherwise itchecks to see if its own data was requested (6B-3) and if so, sendspackets at the specified time (6B-4). It then determines if the datapackets are to be sent to it (6B-5); if not it continues; otherwise itlistens for the data packets at the specified time (6B-6). It also testsfor the reception of data packets designated for it (Step 6B-7) andproceeds with the processes.

Referring to 6C, if Data Packets are heard, it prepares a ReceiveAcknowledgment Packet (6C-1) and listens for a broadcast acknowledgmentfrom the server (6C-2). Continuing it checks for whether it heard theBroadcast Acknowledgment of the sent packets (6C-3) and if heard,deletes the acknowledged packets from its own send queue (6C-4) andsends the receive acknowledgment packet (6C-5). Checking to see if anypackets are left to be sent to the server (6C-6), if yes it reverts tothe timer setup (6A-2) to repeat the process. If not, it checks for anyfurther expected data to transfer (6C-7) and either reverts as above orif nothing further is expected, leaves the PRPstate with the server(6C-8).

The invention has now been explained with respect to specificembodiments. Other embodiments will be apparent to those of ordinaryskill in the art. It is therefore not intended that the invention belimited, except as indicated by the appended claims.

1. In a mesh network having a plurality of communication nodes, whereinone or more nodes may be either a contending node when sending data fortransmission within the mesh network or a controlling node for receivingdata for transmission within the mesh network, a method for accessing acontrolling node, comprising: accessing the controlling node in anon-PRP mode where multiple nodes are not contending for access to thecontrolling node; and accessing the controlling node in a PRP mode wheremultiple nodes are contending for access to the controlling node, thePRP mode comprising: withholding, at a contending node, requests foraccess to a controlling node until receipt, at the contending node, of apoll request packet broadcast from the controlling node, the pollrequest packet containing information indicating availability of acommunication slot; broadcasting from the controlling node to aplurality of contending nodes the poll request packet when thecontrolling node is ready to provide services; directing from thecontending node a poll packet to request access to the controlling node;and broadcasting from the controlling node to all of the plurality ofcontending nodes a control packet containing rules information for eachcontending node requesting access to follow in order to send data to thecontrolling node.
 2. The method according to claim 1, wherein thecontrol packet has rules information from the controlling node thatdirects the requesting nodes when to send and receive data; and whereinthe method further comprises: causing each individual requesting node totransmit local data in turn to the controlling node.
 3. The method ofclaim 2, further including: scheduling each individual requesting nodewhich receives rules information from the controlling node; thereafterreceiving at each individual requesting node acknowledgments from thecontrolling node, the acknowledgments being for correspondingindividually transmitted data packets from the requesting node; andthereafter transmitting from each individual requesting node furtheracknowledgments to receipt of data if data has been previouslytransmitted to it by the controlling node.
 4. The method according toclaim 3, further comprising: purging data packets from a transmittingnode upon receipt of acknowledgment of successful reception of said datapackets.
 5. In a mesh network having a plurality of communicationsnodes, wherein one or more modes may be either a contending node or acontrolling node, an apparatus for requesting access to a congestedcontrolling node, comprising: means for accessing the controlling nodein a non-PRP mode where multiple nodes are not contending for access tothe controlling node; and means for accessing the controlling node in aPRP mode where multiple nodes are contending for access to thecontrolling node, the means for accessing in a PRP mode comprising:means for withholding, at a requesting node, requests for access to saidcongested node while awaiting receipt, at said requesting node, of apoll request packet containing a first datum of information indicatingavailability of a communication slot; broadcasting means forbroadcasting from said congested node said poll request packet when saidcongested node is ready to provide services; and thereafter means atsaid requesting node for directing from said requesting node a pollpacket to request access to the congested node; and means operative tobroadcast a control packet from the congested node to all the requestingnodes having rules information that directs the requesting nodes when tosend and receive data packets.
 6. The apparatus according to claim 5,further comprising: means to cause thereafter each individual requestingnode to transmit its data packets in turn to the controlling node. 7.The apparatus according to claim 6, further including: means at saidcontrolling node for scheduling transmitting times for each individualrequesting node which receives rules information from the controllingnode; means for receiving at each individual requesting nodeacknowledgments of corresponding individually transmitted data packetsfrom the requesting node; and means for transmitting from eachindividual requesting node further acknowledgments to receipt of data ifdata has been previously transmitted to it by the controlling node. 8.The apparatus according to claim 7, further comprising: means forpurging data packets from a transmitting node upon receipt ofacknowledgment of successful reception of said data packets.